Coagulation Disorders USMLE Step 1 Practice Question

A 19-year-old previously healthy male presents to the emergency department with severe bleeding from the gums and diffuse petechiae on his lower extremities. Two hours prior, he underwent an uncomplicated dental extraction for a impacted molar. Vital signs are stable: BP 118/76 mmHg, HR 92 bpm, RR 16/min, temperature 37.1°C. Physical examination reveals petechiae on bilateral lower extremities and oral mucosa, but no hepatosplenomegaly, lymphadenopathy, or neurological abnormalities. Laboratory results are as follows: Platelet count: 8,000/µL Prothrombin time (PT): 12 seconds (normal 11-13.5) Activated partial thromboplastin time (aPTT): 28 seconds (normal 25-35) Fibrinogen: 320 mg/dL (normal 200-400) Hemoglobin: 13.2 g/dL Peripheral blood smear: Normal red blood cell morphology, no schistocytes, no immature myeloid forms The patient denies recent medication use, fevers, diarrhea, and has no history of bleeding disorders. Which of the following is the most likely diagnosis?